US2377453A - Telephone system - Google Patents

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US2377453A
US2377453A US525975A US52597544A US2377453A US 2377453 A US2377453 A US 2377453A US 525975 A US525975 A US 525975A US 52597544 A US52597544 A US 52597544A US 2377453 A US2377453 A US 2377453A
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relay
armature
conductor
line
telephone
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US525975A
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Rhoads Charles Stanley
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AT&T Corp
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American Telephone and Telegraph Co Inc
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Priority to US525975A priority Critical patent/US2377453A/en
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    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04QSELECTING
    • H04Q3/00Selecting arrangements
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04MTELEPHONIC COMMUNICATION
    • H04M5/00Manual exchanges
    • H04M5/04Arrangements for indicating calls or supervising connections for calling or clearing

Description

June 5, 1945. Q s. RHOADS 2,377,453
TELEPHONE SYSTEM Filed March 11, 1944 2 Sheets-Sheet l Calzeal Party Community DaL Office,
INVENTOR asizhmwas Cal Z in Eal'ty ATTORNEY June 5, 1945. Q s RHOADS 2,3
TELEPHONE SYSTEM Filed March ll, 1944 2 Sheets-Sheet 2 INVENTOR B SRhaads M M ATTORNEY ?aienied June 5, 1945 UN TE STATES PATEN .iO F
[7 claims.
This invention relates to telephone, systems and, more particularly, to step-by-step telephone systems. This invention also relates to arrange ments for determining whether or not a subscribers line is busy or out of order. This invention also relates to. arrangements for enabling a telephone operator either to override a line appearingto be busy so that she maydetermine whether the line actually is busy or out of order, or to monitor the busy line, or, ii desired, to converse with the parties to the telephone conversation on the busy line According to present telephone ,practices a manual ofllce-which may be located, for example, in acity and may be attended by one .or more telephone operators-maybe connected to a community dial oillcewhich' is a much smaller oflice located'in an outlying village or hamlet and is generally junattendedh- A subscriber in the communitydial ofiice area may be connected to another subscriber in the area of the community dial 'oiilce in a well-known manner as,-for example, by dialing the latter party in the usual way. During the conversation between the two parties or at any time when the line to the subscriber of the community dial oilice is out of order, as occurs, for example, when the latters receiver is off the hook, it is practically impossible for the operator at the manual oflice to determine whether the subscribers line actually is busy or out of order. Such information would be of value to the operator at the manual oflice for she may have another call awaiting connection to the called party and may, therefore, have considerable telephone equipment tied up while waiting for the busy line to become idle. If she were able to determine definitely that the line is out of order,
she could then release the telephone equipment for other purposes. Moreover, the operator might have an urgent call that must be made to the called party and in that event it would be of value to have an arrangement to enable the operator to override the busy circuit and-connect her own telephone set to the called partys line to converse with that party.
Accordingly, it is one of the objects of this invention to provide a simple and inexpensive arrangement for enabling an operator at, for example, a manual telephone ofiice, to seize a subscribers line extending, for example, from a community dial oflice, to monitor the line while it is busy, or to converse with the parties engaged in the conversation. Such an arrangement will also serve to apprise the operator (and 7 others) as to whether or not the subscriber's line is out of order.
In one of the arrangements to be described hereinafter, a subscriber in a community dial oflice area will be shown connected to another subscriber in the community dial ofllce area, and
the arrangement will include means whereby the operator may verify the busy condition on the already established connection. While the conversation between the parties continues the operator may manipulate a switch, for example, and then dial an additional digit over the line to the called party to connect her own telephone set to the called partys line. The "overriding circuit is completed without in any way interiering with or otherwise ailecting the conversation over the busy line.
It is, therefore, another object of this invention to provide arrangements for enabling an operator to dial a community dial oiiice subscriber whose line is connected to another line and finds it busy and then, while holding the train of equipment she has established to the busy line, to permit the operator to complete her own connection to the busy line by dialing another digit, so that the operator may then monitor the circuit or converse with the parties to the conversation.
These and other objects of this invention will be better understood from the more detailed description hereinafter following when read in connection with the accompanying drawings in a which Figures 1 and 2, when placed adjacent to each other with Fig. 1 above Fig. 2, will illustrate one embodiment of the invention in which a single conductor extending between the master oilice and the community dial oiiice may serve to control an overriding circuit for a busy line.
Referring to Figs. '1 and 2, there is shown a manual oflice MO connected to a community dial ofllce CDO at which there may be a plurality of connector circuits only two of which are shown, and are designated CON and CONz. The arrangements of Figs. 1 and 2 will now be described with reference to the connection of a calling partys telephone set, such as TS1, which may be in the area of a community dial oillce CDO, to a called partys telephone set, such as TSz, which may also be in the area of the community dial flice CDO.
When the calling party TS1 removes his receiver from its switchhook the apparatus at the community dial oflice CDO, generally designated CDE, will act in a well-known manner to seize one of the various connectors such as, for example, CON1 at the community dial ofilce CDO. Apparatus suitable tor this purpose is shown and described in the patent to E. D. Butz, No. 2,021,286, dated November 19, 1935. Immediately after the connector CON1 is seized, the relay A will become operated over a circuit which includes the upper winding of relay A, and ground; The
operation of relay A will complete an obvious circuit for operating relay B. The operation of relay B will cause ground to be applied to the sleeve conductor 8, which extends to the line finder-selector of the equipment MOE in a wellknown manner, the grounding circuit extending from ground at the armature T: of relay B and its make contact, conductor 2|, to the sleeve terminal S. This ground applied to the sleeve conductor will guard the connector CON1 from seizure by any other seelctor and hold the preceding selectors and line finder in the community dial ofiice CDO. The operation of relay B will open the operating circuit of the release magnet RIB which controls; the release of all of the equipment at the. connector CONi, the release magnet RLS' having previously been connected to theback contact or armature T1 of relay B through conductor and the back contact'oi armature Ls of relay-K. The relay B also prepares a circuit for operating the vertical magnet VM as will now be described. 7
After the calling party's telephone set T51 has been connected to the connector (BN1 at the community dial omce CDO by dialing a digit (or digits), thenext digit dialed by the calling party's telephone set T81 will provide a train of pulses for releasing and reoperating' relay A, relay A being operated and released once for each oi the various pulses of the digit dialed by the calling party. The vertical magnet VM is connected to the back contact or the armature of relay A over a circuit which includes battery, the winding of the vertical magnet VM, the armature T: and
back contact of relay H, contacts 21 and 22 of the oil-normal switch VON, conductor 28, the
make contact associated with armature T1 of relay B to the back contact of the armature of relay A which is grounded. The vertical magnet W is connected in parallel to the winding 0! the relay C over a circuit including conductor 22, the back contact and armature L1 of relay K and conductor 3|. The parallel arrangement of the vertical magnet VM and relay C will cause both of those devices to be operated simultaneously. However, relay C as well as relay B are of the slow-release type and hence, they will be held in their operated positions during the pulsing of the first digit. The vertical magnet VM, however, will step its shaft (not shown) in a vertical direction through a number of steps which correspond to the digit dialed.
As soon as the shaft or the vertical ma net W has moved up one vertical step, the ofl-normal switch VON will be moved to its operated position. However, the circuit to the vertical magnet VM will now be completed through the back contact and armatureTa of relay H. conductor 2!, the back contact and armature L1 oi! relay K, conductor 20, conductor 22, conductor 22,
the make contact and armature T1 of relay C,
will now be described.
In response to the next set of pulses corresponding to the third (or next) digit dialed by the calling party's set T81 after connector C081 is seized, the relay A will again release and reoperate once for each of the pulses transmitted as in the case of the previous dial pulses received. This will cause the rotary magnet RJOT1 and the relay E to be operated in series over a circuit which includes battery, the rotary magnet ROTi, the winding of relay E, the back contact and armature T4 of relay H, conductor I8, the back contact and armature T: of relay C, conductor 2|, contacts ll and 20 of switch VON, cond It, the make contact and armature T1 of relay B, the back contact and armature oi relay A, and ground. The subsequent pulses of the third (or next) digit will step the shaft of the rotary magnet ROT1 in a rotary direction in a wellknown manner. The relays B and E, however, will remain operated during these received pulses because these relays are 0! the slow-release type. The relay E when operated holds open the path to the vertical magnet VM, the path to the vertical magnet VM being operated at the back contact of the armature T: oi the relay E. Relay E also completes a path for operating relay H, the operating circuit including battery, the winding of relay H, the armature T: of relay E and its make contact, conductor ll, the armature T4 of relay B and its make contact, and ground. The relay H is then locked in its operated position through the make contact of its own upper armature T1 and hence relay H is held operated even after relay E releases. The opening of the back contact of armature Ts of relay H will open the operating circuit to the release magnet BRLB.
The relay H also opens the operating path for relay E at the back contact of the armature T4 of relay H. Moreover, the operation oi relay H completes apath to-the rotaryselector magnet HOT: at the make contact of armature T; of relay H, this path being connected in parallel with the winding of relay C by conductor 22, the armature L1 of relay K and its back contact, and conductor ll.
As soon as relay E releases, it provides a path for operating relay C in parallel with the selector rotary magnet ROT: upon the subsequent release of relay A. This circuit may be traced from battery andthe winding of relay C, conductor 22, the armature T 0! relay G and its back contact, the armature T: of relay E and its back contact, the make contact and armature T: of relay H, conductor 24, contacts 35 and 28 of switch VON, conductor 3, the make contact 01' armature T1 of relay B, the back contact of the armature of relay A, and then to ground. During the next series of pulses, relay C operates along with the rotary stepping magnet ROT: to control relay G which serves to test the called party's line to determine whether'or not it is busy, as will now be described.
Upon the operation of relay C and magnet ROTz in response to the reception of the pulses of the fourth (or next) dialed digit, a circuit will be completed'irom the winding oi relay 0 to the sleeve terminal 8 extending to the called partys line. This circuit may be traced from battery, the winding of relay G, the make con tact and armature T3 of relay C, contacts 42 and 43 of the switch RON, conductor 44, to the sleeve terminal S. Switch RON is, of course, controlled by rotary magnet ROTz. If ground is found on the latter sleeve terminal S at any time during the pulsing of the fourth (or next) digit, the relay G will become operated. Relay C is of the slow-release type and will remain operated during the remaining pulses of the digit. During this period relay G tests the called lines sleeve terminal S. Should battery be connected to the sleeve terminal S, the relay G will remain unoperated, thereby indicating an idle line condition. Upon the operation of relay G due to the presence of ground on the sleeve terminal S, a source of busy tone will be connected through the make contact and armature T4 of relay G to the calling partys set TSi, the busy tone being transmitted to the set TS1 over the ring conductor R and returned over the tip conductor T. Should relay G become operated, it will open the operating path to relay C at the back contact of the armature T1 of relay G. Once relay G becomes operated it will remain operated until the connector CONl is released by reason of the calling party hanging up.
If the called partys line is idle the relay G remains unoperated. During the received pulses of the fourth (or next) digit, rotary magnet ROTz will be stepped once in accordance with each of these pulses. The rotary magnet ROT: may serve to select any one of a number of codes in a well-known manner for ringing the called partys line, but only one ringing current will be referred to hereinafter for ringing the called partys line. At the end of the received pulses of this digit, relay C will release.
If the called partys line is idle the relay K will become operated over a circuit which includes the ground at the sleeve terminal S, conductor 44, contacts 43 and 42 of the switch RON, the armature T3 and back contact of relay C, the upper winding of relay K, the armature T: and back contact of relay G, the armature T: and make contact of relay B, and ground. The operation of relay K will connect ground through its armature T and its make contact and through conductor 44 to the sleeve terminal S to guard the called partys line against seizure by other connectors such as CONz. The relay K becomes locked in its operated position over a circuit which includes battery, the lower winding of relay K, the armature L1 and make contact of relay K, conductor 46, conductor 40, the armature T4 of relay B and its make contact, and ground. The relay K will lock the connector CON! in its operated position by opening the circuit to its release magnet RLS at the back contact of its armature L3 and the connector CON1 will remain locked until the relay K becomes released. The relay K will connect the called partys telephone line to its own armatures T2 and L1 and in turn to the armatures T5 and T2 of relay F so that the called party's line may become connected to the calling partys line immediately after relay F becomes operated.
The operation of relay K will close a circuit for operating relay J over a path which includes battery, the winding of relay J, conductor 41, the armature T4 and back contact of relay F, conductor 48, the make-before-break contact of armature T1 of relay J, conductor 49, the armature T4 of relay K and its make contact, and
round at GP which is completed through a contact PU on a ringing machine (not shown). The relay K connects battery 15 to the called line over a circuit including the back contact and armature T: of relay J, conductor 55, back contact and armature T5 of relay F, conductor 82, armature T: of relay K and its make contact, conductor 53, and over conductor R to the called subscribers set T32. then back over conductor T, over the make contact and armature L1 of relay K, conductor 52, armature T2 of relay F and its back contact, conductor II, armature T4 of relay J and its back contact, conductor 13, the lower winding of relay F, to ground at GD. This circuit applies pre-trip battery to the called line to cause connector CON1 to cut through and allow the parties to converse immediately if the called party removes his receiver before his bell rings. The operation of relay J will cause ring! ing current to be supplied from the ringing generator RG to the called partys line over a circuit which includes the ringing generator RG, conductor I0, the armature Ta and its make contact, conductor ii, the armature T2 of relay F and its back contact, conductor 52, the armature La of relay K and its make contact, over the tip conductor T to the called partys set T82, then back over the ring conductor R. conductor 53, the armature T: of relay K and its make contact, conductor 82, the armature T5 of relay F and its back contact, conductor 55, the armature T: of relay J and its make contact to the ringing ground GD. This ringing current may be transmltted to the called party until the call is an swered.
When the called party answers in response to the ringing signal the receiver of the called party's set TS: will be removed from its switchhook, thereby causing relay F to become operated. The operating circuit for relay F will include ground at GD, the lower winding of relay F, conductor 14, the make contact and armature T: of relay J, conductor BI, the back contact and armature T5 of relay -F, conductor 82, armature T2 of relay K and its make contact, conductor 53, conductor R, set TSz, conductor T, the make contact and armature L2 of relay K, conductor 52, armature T2 of relay F and its back contact, the make contact and armature T: of relay J, the ringing apparatus RB, the lower winding of transformer TR1, battery and ground. The operation of relay F will cause this relay to become locked, the locking circuit including battery, the upper winding of relay F, the make contact and armature Tl of relay F, conductor 58, make contact and armature T4 of relay B, and ground. The relay F will then connect the calling partys set TS! to the armatures T5 and T: of relay F which were previously traced to the called partys set TS: upon the operation of relay F.
The operation of relay F will also connect talking battery to tip conductor T of the line extending to the called party's set. The two parties may then converse with each other. This battery will be supplied through the lower winding of relay D, conductor 58, conductor 59, the make contact and armature T2 of relay F, conductor 52, the armature L2 of relay K and its make contact over the tip conductor T to the called partys set TSz. Ground will simultaneously be supplied to the ring conductor R extending to the called party's set over a circuit which includes the upper winding of relay D, conductor 80, conductor 6|, the armature T5 of relay'F and its make contact, conductor 82, the armature T: 01'
relay K and its make contact, and the ring conductor R which extends to the called partys set TSz. The connection of battery and ground to the called partys set will operate relay D which in turn will release the relay J. The relay D will also reverse the application of battery and ground to the calling partys set TSi so that ground will now be applied from the upper winding of relay A to the ring conductor R extending to the calling party's set T81, and battery will be connected from the lower winding of relay A to the tip conductor T of the calling partys set TSi.
It has been shown hereinabove that dial pulses corresponding to the called station TS: and emanating from the calling partys station TSi may operate the connector CONi at the community dial ofllce CDO for interconnecting the two stations so that the parties may converse with each other. Should another party (not shown) seek to reach the same called party T52, the additional partys telephone set will be connected to another one of the connectors such as CONz at the community dial oflice CDO. However, the sleeve SS will then be grounded due to the busy condition of the called line and the additional party will not obtain access to the line of the called party. In that case the relay GG of Fig. 2 will be operated over a circuit which includes battery, the winding of relay GG, the armature T3 and make contact of previously operated relay CC, the contacts 42 and 43 of the switch RON: and ground at the sleeve terminal SS. It will be observed that the circuit of Fig. 2 is the same as that of Fig. 1 so far as the connector CON: is concerned but only the essential parts of the connector CON: have been shown to explain the features of the overriding circuit of this invention.
The operator at the manual oilice MO may connect -her telephone set TS: across the tip and ring conductors TI and RR to determine hether or not the called partys line is busy or out of order, or for other purposes. This may be done by the operator inserting a calling cord in a trunk jack, and dialing the called partys number in a well-known manner. The operator will also insert a dialing cord (not shown) in the dial jack after she hears dial tone in the trunk. The operator then will dial the desired number and then she removes the dialing cord from the dial jack, after which she can again listen on the trunk. The operator will then actuate her key KY if the line tests busy and this will complete an obvious circuit to a master control relay MC located at the community dial ofllce CDO. The master control relay MC has a pair of contacts extending to each of the various connectors such as CONi, CON2, etc., for simultaneously actuating certain relay circuits of these connectors so that the operator's telephone set TS: will be bridged across the called partys line that appears to be busy. While holding the connection, the operator will then dial another digit (any digit whatever) to complete the overriding circuit while key KY0 is held operated. This will now be explained.
In response to the dialing of a number corresponding to the called partys line by the operators set TSa-WhiCh is now connected to the connector CONa-the relay GG will become operated over the circuit which, as already noted, includes battery, the winding of relay GG, the armature T3 of relay CC and its make contact, contacts 42 and 43 of switch RONz and the sleeve terminal SS which is grounded because the called partys line is busy. As the master control relay MC becomes thereafter operated in response to the operator's closure of the key KY0, and as the operator dials another digit, the relay AA will become released so as to ground its armature. This will cause relay K to become operated. The circuit for operating relay KK will include battery, its lower winding, conductor 10, the armature T3 of relay MC and its make contact, conductor II, the armature T: of relay GG and its make contact, conductor 12, the back contact and armature of relay AA, and ground. The operation of the relay KK will then connect the tip and ring conductors TT and RR of the called partys line to the armatures T: and T5 of relay FF through the armatures La and T: of relay KK and their make contacts, respectively. The operation of relay KK will then cause relay FF to become operated over a circuit which includes the ground at GD, the lower winding of relay FF, the back contact and armature T4 of relay JJ, armature T2 of relay FF and its back contact, armature L2 of relay KK and its make contact, conductor T1, the calling partys set TSz, conductor RR, the armature T2 of relay K and its make contact, the armature T5 of relay FF and its back contact, the armature T2 of relay JJ and its back contact, resistor Z, battery and ground. Relay FF will be locked as already described with regard to connector CON1. In response to the operation of relay FF the circuit to the called partys set TSz will now be extended to the operators set TS; through the armatures T: and T5 of relay FF and their make contacts. The operators set T53 will now be connected to the telephone circuit previously established by connector CON1. The operator may then determine whether or not the called partys line is busy or out of order due to the removal of the receiver from its hook. Thus the busy line may be seized and its condition tested by the operator first dialing the number corresponding to the called party's station, then operating key KY0, and then dialing another digit to complete the connection to the busy line.
It will be observed that the master control relay MC includes a plurality of armatures each of which is assigned to but one of the various connectors and, as there would be several connectors in an ordinary community dial oflice, the relay MC would require as many armatures as there are such connectors in the ofllce. The operation of the master control relay MC in response to the manipulation of the key KY0, however, will permit the operation only of the relay such as K of connector CONz, which receives an additional or fifth digit dialed by the operator for the purpose of overriding a busy condition. Thus, the only subscriber's line seized will be the one which responds to the groups of dial pulses emanating from the operators telephone set TSz. The last of these dial pulses will operate a relay such as FF of connector CONz, for example, to complete a path to the busy partys line. Thus the operator will be bridged across the telephone line of the particular party that is dialed by the operator and the connection will be completed only when the operator actuates her key KY0 and dials an additional digit.
While this invention has been shown as applied to a step-by-step telephone system having an additional conductor interposed between the community dial oflice CD0 and the manual ofllce M0 for actuating the master control relay MC, similar operation of the master control relay may be effected over a loop dial trunk, or over a composite trunk dial leg, or by other means, as will be apparent to those skilled in the art.
While this invention has been shown and described in certain particular embodiments merely for the purpose of illustration, it will be understood that the general principles of this invention may be applied to other and widely varied organizations without departing from the spirit of the invention and the scope of the appended claims.
What is claimed is:
1. In a telephone system, the combination of a telephone line interconnecting two telephone stations, and means to monitor over said telephone line, said means including means responsive to dial pulses corresponding to one of said interconnected telephone stations and to an additional dial pulse to seize the busy telephone line without interfering with communication over said telephone line, the busy telephone line being seized for communication thereover only after said additional digit is dialed.
2. In a telephone system, the combination of a telephone line, a first subscriber's set connected to said line, a second subscriber's set, means responsive to predetermined dial pulses to connect said telephone line to said second subscriber's set, an operators set, and means responsive to predetermined dial pulses transmitted from said operator's set and to an additional pulse to connect said operators set to said second subscriber's set, the second subscriber's set being seized for communication therewith only after said additional pulse has been transmitted.
3. In a telephone system, the combination 01 a first telephone set, a second telephone set, a line, means responsive to predetermined dial pulses produced by said first telephone set to connect said first telephone set to the second telephone set over said line, an operators set, and means to connect said operators set to said line to determine whether said line is busy, said latter means including means responsive to additional pulses corresponding to said predetermined dial pulses and to an additional pulse to seize said line, said line being seized for communication thereover only after said additional pulse has been transmitted.
4. In a telephone system, the combination of a plurality of connectors each of which may serve to connect a pair or telephone stations to each other, a calling telephone station, a called telephone station, a third telephone station, means responsive to predetermined dial pulses emanating from the calling station and corresponding to the called station to connect said calling station to said called station through one of said connectors, means responsive to the same dial pulses emanating from the third telephone station and corresponding to the called station to return a busy signal to the third station over another of said connectors, and means responsive to an additional dial pulse of the series of dial pulses transmitted to the latter connector to seize the circuit interconnecting the calling and called stations for monitoring said circuit.
5. In a telephone system, the combination of an attended office, an unattended office, a subscribers circuit connected to said unattended office, means to dial said subscriberscircuit from the attended ofliceand to determine whether said subscriber's circuit is busy, and meansto dial an additional digit when said subscriber's circuit tests busy to seize said subscriber's circuit without interfering with whatever conversation may be going on over said subscriber's circuit, said busy subscriber's circuit being seized for conversation thereover only after the additional digit has been dialed.
6. In a telephone system, the combination of an attended oflice having an operators set, an unattended oflice, a subscriber's circuit connected to said unattended oflice, means to monitor the subscribers circuit from the attended office, said means including means responsive to dial pulses corresponding to said subscriber's circuit to return a busy signal to the operators set at said attended oflice, and means responsive to additional dial pulses to connect said operators set to said subscriber's circuit for communication purposes without interfering with any conversation over said subscriber's circuit.
'7. In a telephone system, the combination of an unattended telephone oiiflce, two subscriber's telephone sets connected to each other through said unattended ofllce, an attended telephone office connected to said unattended ofllce, an operators telephone set at said attended oflice having means for producing dialing pulses for signaling one of said subscriber's sets, equipment at said unattended ofllce which may be operated by said dialing pulses, a circuit interconnecting said unattended ofllce with said attended ofllce, means controlled at said attended ofllce to operate said sets.
CHARLES STANLEY RHOADS.
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Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2491291A (en) * 1945-12-03 1949-12-13 Automatic Elect Lab Common trunk selecting means for all relay telephone switches
US2516645A (en) * 1947-02-12 1950-07-25 Stromberg Carlson Co All-relay automatic and manual telephone system having butt-in and alarm features
US2524131A (en) * 1946-10-18 1950-10-03 Automatic Elect Lab Automatic telephone system incorporating mixed service connectors
US2562362A (en) * 1947-11-04 1951-07-31 Automatic Elect Lab Testing system employing test distributor switches and test connector switches
US2621257A (en) * 1945-12-03 1952-12-09 Automatic Elect Lab Relay automatic telephone system
US2665375A (en) * 1948-09-09 1954-01-05 Gen Electric Co Ltd Radio telephone system
US2753401A (en) * 1954-03-30 1956-07-03 Gen Dynamics Corp Busy verification
US2785237A (en) * 1954-04-05 1957-03-12 Gen Dynamics Corp Howler control circuit
US2988602A (en) * 1955-12-27 1961-06-13 Gen Dynamics Corp Final selector for a telephone system

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2491291A (en) * 1945-12-03 1949-12-13 Automatic Elect Lab Common trunk selecting means for all relay telephone switches
US2621257A (en) * 1945-12-03 1952-12-09 Automatic Elect Lab Relay automatic telephone system
US2524131A (en) * 1946-10-18 1950-10-03 Automatic Elect Lab Automatic telephone system incorporating mixed service connectors
US2516645A (en) * 1947-02-12 1950-07-25 Stromberg Carlson Co All-relay automatic and manual telephone system having butt-in and alarm features
US2562362A (en) * 1947-11-04 1951-07-31 Automatic Elect Lab Testing system employing test distributor switches and test connector switches
US2665375A (en) * 1948-09-09 1954-01-05 Gen Electric Co Ltd Radio telephone system
US2753401A (en) * 1954-03-30 1956-07-03 Gen Dynamics Corp Busy verification
US2785237A (en) * 1954-04-05 1957-03-12 Gen Dynamics Corp Howler control circuit
US2988602A (en) * 1955-12-27 1961-06-13 Gen Dynamics Corp Final selector for a telephone system

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